Process for fusing xerographic images

ABSTRACT

A PROCESS FOR FUSING AN ELECTROSCOPIC TONER IMAGE TO THE SURFACE OF A SUPPORT IN WHICH THE SUPPORT IS MOVED RELATIVE TO A STATION WHERE A NONSOLVENT VAPOR IS APPLIED TO THE SUPPORT. THE TONER IMAGE IS FUSED BY THE SUPPORT BY THE HEAT RELEASED BY THE EXOTHERMIC CHANGE OF STATE OF THE VAPOR DUE TO ITS CONTACT WITH THE SUPPORT AND TONER.

W. 5- WHITE ET AL PROCESS FOR FUSING XEROGRAPHIC IMAGES March 2, 1971 Filed March 17, 1969 WILL/AM WHITE WILL IAM F GARBE INVENTORS AGENT PROCESS FOR FUSING XEROGRAPHIC IMAGES William E. White and William F. Garbe, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y. Filed Mar. 17, 1969, Ser. No. 807,831 Int. Cl. B44d 1/094; G03g 13/20 US. Cl. 11717.5 6 Claims ABSTRACT OF THE DISCLOSURE A process for fusing an electroscopic toner image to the surface of a support in which the support is moved relative to a station where a nonsolvent vapor is applied to the support. The toner image is fused to the support by the heat released by the exothermic change of state of the vapor due to its contact with the support and toner.

FIELD OF THE INVENTION The present invention relates to a process for fusing an electroscopic powder image to the surface of a support bearing the image and, more particularly, to a process in which such fusing is accomplished by utilizing the heat of vaporization of a liquid having a boiling point above the fusng temperature of the toner forming the image.

DISCUSSION OF THE PRIOR ART There are three generally known processes or methods for fusing electroscopic toners to a support. The prior art generally includes the processes or methods known as vapor fusing, contact fusing and radiant fusing.

Vapor fusing requires that a liquid be used that is a solvent for at least the binder, if not for all ingredients comprising an electroscopic toner. In this process, the liquid at least partially dissolves the resin binder so that the toner can be partially or completely embedded in the binder which can be considered to be part of the support. Two major objections with respect to this technique are: (1) the material must be dry when it leaves the fusing station to avoid offsetting of the toner onto the feed or guide rolls which can only be prevented by using Teflon (polytetrafluorine)-covered rolls and silicone oil; and (2) the device itself must be tightly sealed because the solvents are often quite toxic and harmful to the operator and may have an objectionable odor. Another difficulty is that when the solvent is vented off, it is generally not recoverable and, hence, presents an additional expense that must be considered.

Contact fusing, while very attractive in several respects, has very special problems in that heated rolls are required which require a relatively long warmup time and special controls to maintain the rolls at an optimum fusing temperature. Offsetting of the toner from the image area to the rolls also presents a problem which, as mentioned above, can only be overcome by covering the surface of the rolls with a material such as Teflon, and applying an offset preventing liquid such as silicone oil, to the rolls. It can be readily appreciated that very special requirements are imposed on the apparatus used for this system of contact fusing.

The use of radiant heat such as that derived from infrared lamps, electric coils, etc., while having a somewhat faster warmup time, must have an extremely high power requirement in order to heat these elements to the proper fusing temperature at a very rapid rate. In general, these elements are not energized, or only partially energized, while the machine or device is in a standby condition. The main objection to this type of fusing device is that it presents a potential fire hazard, and safety control devices are needed to avoid this risk. Also, it is difficult to move the copy at speeds that will always result in good Patented Mar. 2, 1971 fusing of the toner to the copy in all image areas, because the more dense and solid image areas may absorb enough heat to char the support therebeneath, whereas the fine line image areas lose their heat to the support therebeneath and do not absorb sufficient heat to thoroughly fuse to the support.

SUMMARY OF THE INVENTION One object of the present invention is to provide a process for fusing a powder-toned Xerographic image to a support carrying the image by which the support can be moved at relatively high speeds with respect to a fusing medium.

Another object of the invention is to provide a process for fusing a powder-toned xerographic image to a support carrying said image on a continuous basis and by which the support is moved relative to the vapors formed by a liquid having a high heat of vaporization and a boiling point above the melting point of the toner particles.

Still another object of this invention is to provide a process for fusing a powder-toned xerographicimage to a support carrying the image by which the support can be moved relative to the fusing medium with the image facing away from or toward the fusing medium depending on whether the support is one which will or will not absorb the fusing medium.

Other objects and advantages of the invention will be readily apparent to those skilled in the art when the more detailed description set forth hereinbelow is read in conjunction with the attached drawing.

The above objects and advantages of the invention are obtained by a process for fusing an electroscopic toner image to a surface of a support in which the support is moved relative to a vapor fusing station wherein the heat supplied for fusing the toner to the support is generated by the heat of vaporization of a liquid that is released by a vapor as it condenses upon contacting the cooler support. The liquid used for providing the vapor is a nonsolvent for the toner, which does not attack or degrade the image quality. Also, the liquid is one that has a high heat of vaporization and a boiling point that is higher than the melting point of the toner particles. The invention is applicable to most vapor fusing apparatus disclosed in the prior art. In practice, the liquid is heated in an essentially sealed container to its boiling temperature, the liquid being displaced from the plane through which the support is moved for fusing. The vapor rises in the container and at an orifice in the container, over which the support is moved, contacts the support and gives up heat as it condenses. This heat is sufficient to insure good fusing of the toner at a high rate of support movement. The vapor, as it condenses, can be collected and returned to the container. If the support is one that readily absorbs liquids, all of the liquid need not be removed from the support, because the moisture still present in the support as it emerges from the fusing station does not affect the toner particles. In other words, the image is already fused and the support, if in sheet or web form, can be immediately handled, stacked and so forth, without smearing or smudging the image.

DESCRIPTION OF THE DRAWING Reference is now made to the accompanying drawing wherein the like reference numerals designate like parts and wherein:

FIGS. 1 and 2 are schematic representations of fusing devices useful in employing the invention and show the manner in which an imagebearing support can be moved relative to a liquid being vaporized and the manner in which the condensate can be recovered and returned to the system.

3 DESCRIPTION OF THE PREFERRED EMBODIMENT A support in the form of a sheet, or a continuous web, comprises a conductive backing member and a layer of photoconductive material on one surface of the member. As is well known in the art, the backing member can comprise a metallic foil or a material, such as a. conductive paper. The photoconductive material comprises a resin binder in which a photoconductor, such as zinc oxide, is contained. Upon imagewise exposure, as is well known, a latent electrostatic image is produced on the surface of the photoconductive material. When electroscopic toner particles of the proper polarity are applied to the imagebearing surface of the support the particles will adhere thereto in the areas where there is an electrostatic charge, thereby producing a visual image. However, to provide an image that is usable, that is, one in which the toner particles are firmly fixed to the layer of photoconductive material or to another support by suitable transfer techniques known in the art, it is necessary to fuse the toner image to the support. In other words, the toner must be fixed to the image support.

Since the powder toned Xerographic image must be heated to a temperature sufficient to fuse the toner particles to the support, whether it be a photoconductive layer on a backing member or a sheet or web of insulating material, the liquid that is used in accordance with the invention must be one that upon condensing gives up sufficient heat to accomplish the fusing. Consequently, the liquid must be a nonsolvent for the support or toner, have a high heat of vaporization, and have a boiling point that is higher than the melting temperature of the toner. Some such materials that possess these characteristics include water, ethylene glycol, their mixtures and the like. The melting point of the toner that is used will determine the liquid that can be used. Water is preferred as the fusing liquid in conjunction with a compatible toner when the support is a paper or a similar material having an aflinity for liquid. In this case, the liquid is very inexpensive and there is little, if any, need for providing a tight system. In other words, any escaping vapors (steam) will have substantially no effect on the machine, the environment, or the personnel.

From the more detailed description which follows, it will be readily apparent that a support having a powdertoned Xerographic image can be moved past a fusing station at a relatively high rate of speed to accomplish satisfactory fusing of the toned image. The combination of a hot vapor together with the vapor condensing and giving up its heat, which occurs in a relatively short time, imparts sufficient heat to the sheet or web to effect good fusing of the toner. While a cooling area adjacent the fusing chamber is not absolutely necesary, such an area is of help in that any offsetting of the toner to the rolls engaging the fused image surface is eliminated.

The temperature of the vapor chamber and of the vapor in the chamber will vary in accordance with the boiling point of the particular liquid used, e.g., from about 100 C. for water to about 200 C. for the ethylene glycol. It is understood that the toner to be used must have a melting point below the boiling point of the liquid.

With reference to FIG. 1, the support comprises an electrically conductive backing member 11 and a layer of photoconductive material 12 with a powder toned xerographic image 13 on the surface of the material 12. The support 10 can also comprise an insulating material to one surface of which a powder toned xerographic image has been transferred. The support 10 can be in the form of a single sheet having one or more images or of a web having a plurality of images arranged thereon in a longitudinal and/or a transverse direction.

A receptacle 15 contains a liquid 16 which is heated by an element 17, the latter being a hot plate or any other form of suitable heating means for raising the liquid 16 4 to the required temperature. The receptacle 15 is provided with a plug 18 having a slot 19 which extends across the path of movement of support 10. The support 10 is moved across receptacle 15 and relative to the slot 19 by any suitable means and maintained in close proximity to the outer surface 20 of plug 18 by rolls 21 and 22.

As shown in FIG. 1, the image 13 is on the surface of the support 10 that faces slot 18. If the support 10 will not readily absorb liquids, that is, it is generally impermeable to liquids, then the image must be in this relationship to the slot 18 to obtain good fusing of the toner. In this case, the support 10 can comprise a metallic backing member and a layer of photoconductive material. Further, the liquid must be a nonsolvent of the resin binder in which the photoconductor is retained and the condensate can be removed for reuse, providing a circulatory type of system is used. In the event the support 10 is of paper with a powder-toned Xerographic image on one surface thereof, then the image can face either toward or away from the outer surface of plug 18. A paper support would normally be permeable to liquids so that the image can face toward or away from plug 18 and the condensate can be squeegeed off the image or non-image surface for reuse in the system.

As described above, the liquid 15 is heated to and maintained at its boiling temperature, thereby providing a hot vapor which is incident on the surface of support 10 facing plug 18. As the vapor strikes this surface, it condenses, releasing its heat of vaporization to the surface plus a smaller amount of heat that is released as the condensed liquid cools to the final equilibrium temperature of the support-liquid interface. If suflicient hot vapor is available, it will continue to condense on and heat the support until the temperature of the support surface equals that of the vapor which, in turn, may be as hot as the boiling point of the liquid 15. This heat is suliicient to cause the toner particles to fuse to the support irrespective of the surface facing the plug 18. In other words, the heat is sutficient for obtaining good fusing if the vapor is incident directly on the image or on the support. It has been found that good fusing results with support speeds of 4 to 11 inches per second which means that the support can be over the slot 19 for approximately 4; to second. With such speeds, the support is moving at such a rate that the complete thickness of the support does not reach the fusing temperature.

In FIG. 2 another embodiment of the invention is shown, the support 10 being the same as that described above with respect to FIG. 1. The liquid 30 is contained in a receptacle 31 and is carried toward the support 10 and through a heating chamber 32 by a wick 33. The chamber 32 is formed in a casing 34 which also contains heating elements 35 which are controlled by a thermostat 36. The casing 34 is provided with a well 37 over which the support 10 is moved by roll 38 at one end and rolls 39 and 40 arranged at the far end of the cooling sector, designated by the numeral 41, which is positioned adjacent the other end of casing 34. The well 37 is gen erally enclosed with a cover 42, openings being provided at opposite ends for ingress and egress of support 10. The cooling sector 41 is connected to receptacle 31 by line 43. A liquid level control 44 is also connected to receptacle 31 for maintaining a predetermined liquid level therein. The casing 34 and the cover 42 can be made of a heat-insulating material or lined with such a material.

As in FIG. 1, the image 13 can face toward or away from the vapor source, that is, liquid 30 and wick 33. The vapor heat evident on the support 10 as well as the heat given up by the vapors upon contacting support 10, as described with respect to FIG. 1, cause the fusing of the toner to the support. The support is cooled in the sector 41 and the rolls 39 and 40 also serve to squeegee the condensate from the support so that it is returned to the receptacle by the line 43.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention.

We claim:

1. Process for fusing an electroscopic powder image to the surface of a support bearing said image, comprising:

exposing said support to the vapors of a liquid that is a nonsolvent for the electroscopic powder, said liquid having a boiling point above the melting temperature of said powder and a high heat of vaporization;

whereby said powder image is fused to said support by the heat supplied by the condensation of said vapors upon exposure to said support.

2. The process in accordance with claim 1 wherein the imagebearing surface of said support is exposed to the vapors of said liquid.

3. The process in accordance with claim 1 wherein the surface opposite said imagebearing surface is exposed to the vapors of said liquid.

4. The process in accordance with claim 1 wherein said liquid is ethylene glycol.

5. The process in accordance with claim 1 wherein said liquid is water.

6. Process for fusing an electroscopic powder image to the surface of a support bearing said image, comprising:

heating a liquid, that is a nonsolvent for the electroscopic powder and has a boiling point above the melting point of said powder with a high heat of vaporization, to the boiling point of said liquid; and

moving said support relative to the vapors produced on vaporization of the said liquid, with the imagebearing surface of said support in direct contact with said vapors;

whereby said powder image is fused to said support by the heat supplied by the condensation of said vapors upon exposure to said support.

References Cited UNITED STATES PATENTS 3,140,160 7/1964 Carlson 1l72l RALPH S. KENDALL, Primary Examiner R. M. SPEER, Assistant Examiner US. Cl. X.R. 117-21, 119.8 

